It will be understood that disk drive magnetic storage devices must write and read information with very low error rates. The primary components of a disk drive system which determine the signal to noise ratio, which in turn determines the error rate, are the magnetic head and the disk recording medium.
In the prior art, considerable testing is done on each of these components in an attempt to assure that the combination thereof will work at an acceptably low error rate. Because these components interact in complex ways, this screening of individual elements can unnecessarily eliminate some combinations of components which might work successfully together, thus needlessly increasing the cost of the disk drive. Furthermore, in disk drives using bands of different recording density, individual component testing becomes prohibitably complex and expensive.
A second type of problem is that with high volume manufacturing, adjustment to optimize performance of individual devices may be undesirable, and indeed, with miniature disk drives it may be physically impossible to incorporate such adjustments due to the small size of the equipment.
A third problem is that as components age, the error performance may deteriorate. Disk drives are typically embedded in a compact computer unit, so that service and adjustment thereto are not practical or cost effective.
U.S. Pat. No. 5,121,262 to Squires et al. partially addresses the first-mentioned problem above by providing a method that adjusts certain parameters and fixes a single set of adjustments. A serious problem with this method is that no means are described to optimize each recording zone, nor is the adjustment available during normal operation of the system.
A further problem with such a method is that the normal error rate is so low that a very long time is required to measure the errors and analyze the effect of any adjustment to the system. For example, a typical disk drive with 160,000 data bits per track having an error rate of one bit in 10.sup.8 will produce a single error on the average of once every ten seconds. If ten samples are required for statistical reliability, a disk drive with four adjustment routines each with eight steps would require nearly 53 minutes per disk surface. If this optimization were required for multiple-zone recording for a disk drive with more than a single recording surface, it is evident that the method could take several hours, which would be impractical for calibration except at the point of manufacture.
U.S. Pat. No. 5,053,892 to Supino et al. discloses a method of disk drive operation wherein the head position may be adjusted in an attempt to improve its centering over the track of data. The method further discloses attempting to change the domain configuration (and thus the permeability of the head poles) to enable the head to improve its reading operation. Rather than a methodical approach to improving the operation of the system, this patent discloses a method wherein after a certain number of failed attempts are undertaken, the device is declared uncorrectable.